A vehicle air conditioning system performs two primary functions: temperature regulation and dehumidification. These functions and the vehicle fuel economy can usually be enhanced by drawing at least a portion of the inlet air from the cabin of the vehicle after an initial cool-down period of operation because the introduction of cabin air generally reduces the enthalpy of the inlet air mixture. In most manually controlled systems, introducing cabin air into the inlet air-stream is achieved with a mechanical bleed device designed to maintain a given proportion of cabin air and outside air. In some manually controlled systems and most automatically controlled systems, inlet air mixing is achieved with an inlet air mixing device (such as controlled door in an inlet duct), with the inlet air mixture comprising predominantly outside air in a normal mode and predominantly cabin air in a recirculation mode. In the manually controlled versions, the operator selects either the normal or recirculation mode, while in the automatically controlled versions, the selection is performed by a system controller based on various input parameters such as the desired cabin temperature, the measured cabin temperature, and so on. In any event, it is commonly recommended that the usage of cabin air recirculation be limited in order to more effectively purge odors and smoke generated in the cabin, and in order to prevent intrusion of exhaust gases under certain conditions. Additionally, extended operation in the recirculation mode can tend to lower the relative humidity of the cabin air to an uncomfortable level.